5D Runge-Lenz Vector from Symplectic Reduction of 8D Harmonic Oscillator

Abstract

We derive the Runge-Lenz vector of the five-dimensional Kepler problem from the eight-dimensional harmonic oscillator through symplectic reduction. By rewriting the moment maps of the harmonic oscillator in terms of five-dimensional gamma matrices and the $\mathfrak{su}(2)$ generators associated with the symplectic reduction, we identify the moment map expected to yield the Runge-Lenz vector. We then perform the reduction with respect to the SU(2) symmetry, derive the five-dimensional Kepler Hamiltonian, and show explicitly that the identified moment map reduces to the Runge-Lenz vector.